Hyperledger Fabric design

Question

I am new to the area of DLTs or "blockchain" and I am trying to create an application on top of Hyperledger Fabric. Before I describe my use case, I need to mention that due to my use case's nature I need a private & permissioned "blockchain" which justifies the choice of Fabric (I am aware of other platforms e.g. Corda, private Ethereum, but Fabric seems to match my use case better).

Use Case

My use case consists of two different types of participants. A number of organizations (which upload and share information about individuals on the distributed ledger) and a client who can query information about an individual. The client should not be able to see the transactions uploaded by the organizations and will not have write rights on the DL. He has read-only rights. Moreover, the organizations trust each other and there is also a level of trust between them and the client.

Design thoughts

Based on what I've read, I was thinking of creating a DL network that includes all of these parties and use channels which, based on the documentation, can be used to create a grouping among a number of participants (the organizations in my case) thus "hiding" the transactions from the parties which are not included in this group (the client in my case).

However, later I read about chaincode (a.k.a. smart contracts) which:

can be invoked by an application external to the blockchain when that application needs to interact with the ledger

which confused me since if the "blockchain" can be queried from an external entity, that probably means that the client should not be included in the trusted network.

Am I headed in the wrong direction (design-wise)?

Answer 1

Based on your description, Hyperledger Fabric channels sound like a good solution. You should also familiarise yourself with private data collections, as this is another way of hiding some of the data from some peers. Which option is best for your scenario will depend on how your datasets are structured, and whether you also need to keep the data private from the orderer.

Clients are not part of the network. They query the blockchain by connecting to a peer and then requesting data from that peer. They can then only access the data visible to that peer (which is stored locally by that peer). So, it is not possible for a client to access more data than is available to the peer the client is connected to.

In your example, you would have a "client" organisation, with at least one peer. This peer would be part of the network, and your client application would then connect to it for access to data on the ledger (typically using the Hyperledger Fabric Node SDK).

There are two types of chaincode in Hyperledger Fabric.

• User Chaincode (often just referred to as "chaincode") is used to update the ledger for a channel, and is only installed on those peers which require it (i.e. endorsing peers). Since your "client" peer would not be an endorsing peer, it would not have access to the user chaincode for the channel.
• System Chaincode which all peers have access to, provides (among other things) an interface to allow queries to be run against the ledger.